Process of making flaked lead acetate



Patented May 30, 1933 UNITED STATES RALPH E. LAWRENCE, F WICKLIFFE, O HIO, ASSIGNOR TO THE GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF DELAWARE IPROCESS OF MAKING FLAKED LEAD ACETATE No Drawing. Original application filed October 14, 1929, Serial No. 399,710. Divided and this application filed February 5, 1331. Serial No. 513,784.

This invention relates to lead acetate in the form of thin flakes and to processes of obtaining it in said physical form.

Neutral lead acetate crystallizes with :8 mols of water of crystallization. It is commonly made by concentrating a clear solution of lead acetate to a high gravity, say 85 B., and then running the heavy syrup into pans. It forms under these circumstances super-cooled masses which remain for some time in the fluid state and then solidify as a whole to hard and compact, large size agglomerates. The further handling of this product involves much manual labor in the removal from the pans, breaking up of the blocks and packing which creates a serious occupational health hazard. V

I have now found a process whereby lead acetate can be produced in a physical form in which it is easy to handle, obviating the necessity of breaking it up or disintegrating it and doing away with much manual labor and its inherent disadvantages. The so produced lead acetate appears in the form of thin, compact, co-herent flakes in which physical form I am not aware that lead acetate has ever heretofore been produced, though it has in this form considerable practical advantages over the usual broken technical lead acetate.

Concentrated lead acetate liquors have the peculiarity of forming undercooled liquors which may remain for undetermined periods of time in this physical state; they then set 35 and harden quickly into solid masses. If i such liquors are run upon a movingcooling l surface such as the revolving cylinder of a drum cooler no provision can be made for the regular removal of solidified lead acetate; in some instances the liquor would not have solidified before reaching the removal device, in others it would already be in such a state-of solidification that the product would break up on removal into an irregular powder with much dusting, which would create either a serious health hazard or necessitate extensive dust collecting equipment.

I have found that by inducing the crystallization of concentrated lead acetate liquor 50 films solidification takes place gradually,

pa sing through a stage where the lead acetatc has a waxy consistency. The film can this stage easily be scraped off, whereby it breaks up into small, co-herent shavings like flakes, which do not dust, and solidify finally into hard and compact individual flakes.

A. technically very convenient manner of inducin the solidification of a syrupy lead acetate nlm is to bring it into contact with solid lead acetate and I found that this is particularly easily achieved by first coating a cooling surface with a thin layer of solid lead acetate; the syrupy melt of additional lead acetate applied thereto solidifies gradually passing through a waxy state of consistency. A thin film of waxy lead acetate so formed. It does not, while in this state adhere very firmly to the base layer of solid acetate; when scraped off from said solid layer it separates into non-dusting, nonsticky soft flakes, or shavings, which soon solidify into hard, co-herent flakes of more or less regular shape, usually about one millimeter thick, several millimeters long and a few millimeters wide.

The product in this flake form weighs, when packed, from to lbs. per cubic foot packing space; the flakes are easily soluble and conveniently handled by the consumer.

The flaking of lead acetate according to my novel process is conveniently achieved on socalled drum solidifiers or drum coolers. This type of apparatus consists in its essential 855 parts of a feeding device, such as-a trough or feeding channel containing the. liquidto be solidified, of a rotating cylinder which is in contact with the liquids in the feeder and on rotation picks up some of the liquid sea which adheres to its surface and solidifies thereon in contact with the atmosphere and of a scraping device which removes the solidified material from the surface of the drum. Provision is usually made to cool the inside T: of the drum with a gaseous or liquid cooling fluid.

In preparing my novel flaked product I I used a-solution of lead acetate of 85 B. at C. Some of this liquor was poured upon 100V the surface of a rotating cooling drum and rubbed over the surface of the drum by means of a brush forming a uniform layer thereon which crystallized and adhered to the drum.

5 The knife edge of the scraper arrangement was then so adjusted as to leave a thin coat of this original, solid lead acetate on the drum.

A very convenient manner of feeding the concentrated lead acetate liquor upon the drum cooler coated as described above with a thin layer of solid lead acetate was found to consist in running a stream of the liquor down an incline which ends in a piece of sheet steel fitted closely to the layer of solid acetate, at the back, underside of the drum, tangent to the surface and parallel to the axis of the drum. The acetate liquor accumulates in the channel formed between the steel sheet and the drum and is from there picked up during revolution forming a liquid film upon the original base layer of solid acetate and solidifies uniformly thereon.

The 85 Be. acetate liquor when fed in this manner to the drum started to solidify after a few seconds in contact with the solid acetate, which serves as a seeder. The speed of revolution of the drum and the cooling were adjusted to give the lead acetate film about 23 seconds time between its formation at the feeder and its removal by the scraper. It had during this time solidified to a waxy, non-sticky consistency and it broke off at the knife in the form of soft, non-sticking flakes which in a few minutes after leaving the scraper set to compact, hard flakes. The packed weight of the product from this par ticular run was 67 lbs. per cubic foot; it analyzed 55.8% Pb. whereas the theory for rmo mon srigo is 54.6%, indicating a slight drying action during the process, which, however, is not objectionable. The packed weight of the product made by my process varies generally between the limits of about and 70 lbs. per cubic foot. The

solidification of the lead acetate liquor is so conducted that it takes place gradually through a stage where ithas a waxy, nonsticky consistency, at which stage the acetate is separated into flakes.

It is further understood that the term lead 80 acetate is used herein with its usual commercial meaning of neutral lead acetate contain ing in the neighborhood of 3 mols of water of crystallization.

This application is a division of my application Serial #399,? 10, filed Oct. 14, 1929,

for lead acetate, now Patent Number 1,842,908.

I claim:

1. The process of producing flaked lead acetate which comprises forming a film of liquid lead acetate, inducing solidification to take place gradually whereby the lead acetate passes through a stagewhere it has a waxy consistency, and breaking up the lead acetate at said stage into flakes.

2. The process of producing a flaked lead acetate wihch comprises forming a film of liquid acetate in contact with solid lead acetate, allowing said liquid film to solidify gradually, and removing and breaking up said film before it is completely solidified.

3. The process of producing flaked lead acetate which comprises forming a film of liquid lead acetate in contact with solid lead acetate upon a surface having a rotary direction of movement and removing the material from the surface when the material has solidified only to a waxy consistency whereby it breaks up into particles which solidify to hard, compact and coherent flakes.

In testimony whereof, I afliX my signature.

RALPH E. LAWRENCE. 

